Commercial wireless communication systems have become very popular. In particular, one such system, referred to as a cellular system, is used widely for communication between portable telephones carried in automobiles by persons. In such systems the power of transmitters located in a communication region define so-called "cells". When an active wireless portable terminal moves from cell to cell, this is sensed and control of a call in progress is "handed off" from the first to a succeeding cell.
Other types of wireless communication systems are for example a cordless telephone in which a single wireless handset communicates with a single base station on one of several designated frequencies, a so-called CEPT system, which involves analog FM operation utilizing 40 channel pairs and dynamic channel pair allocation, a Telepoint system, presently implemented in the U.K., which provides a simple one-way service allowing direct radio access to base stations situated at fixed locations such as railroad stations, shopping centers, gas stations, restaurants, hotels, etc., and others. Standards for such services have evolved, such as the so called CT-2 and CT-3 standards.
Such systems all have basic limitations in their channel capacity; only a limited number of channels can be made available within a given region. Therefore the systems are not feasible in a region in which there is a high density of users, such as several thousand persons within a high rise building within the high density core region of a city, which building may be adjacent another housing several thousand persons. In such case, not only is there a high demand for the limited channel capacity, but due to the nature of building structural materials, reflections and null regions and phase shifts abound, affecting the qualities and reliability of communication as the portable wireless terminal is carried while in use.
In Canadian Patent 1,247,266 issued Dec. 20th, 1988, invented by Michael J. Carey and Adrian J. Anderson, a system for use in such environments is described, using both wire antenna and leaky cable antennae, and using spread spectrum communication. The system substantially reduces or eliminates null regions, and because as in one embodiment the antenna is a leaky cable which is located relatively close to the portable wireless terminals, e.g. contained in the ceiling, the radiated power can be low, substantially eliminating or reducing the effects of reflections and null regions caused by the building structure. The leaky cable (leaky feeder) could be strung to saturate the entire communication region fairly evenly with electromagnetic energy.
A leaky feeder distribution system for office communication is also described in the article "Cordless Telecommunications in the U.K.", by R. S. Swain, published in the BRITISH TELECOM TECHNICAL JOURNAL, Vol. 3, No. 2, April 1985. Here it is stated that the feeders are a particularly attractive option for the wireless PABX concept. While leaky feeders can be successfully used in an office communication region, they have heretofore not been able to be used to locate the position of the portable terminal.